1. Field of the Invention
The present invention relates to a power supply apparatus for changing-over a plurality of batteries from a parallel connection to a series connection and vice versa. More particularly, the present invention relates to a power supply voltage change-over apparatus for a vehicle which connects two batteries in parallel when an ordinary load is used or the two batteries are charged, and which connects the two batteries in series when a large power electric load is actuated.
2. Discussion of Background
A conventional power supply voltage change-over apparatus is described with reference to FIG. 4 in a block diagram. In FIG. 4, reference numerals 1a and 1b designate batteries mounted on a vehicle, numeral 2 designates charging generator for charging the batteries, numeral 3 designates an ordinary electric load, numeral 4 designates a parallel/series connection change-over relay for changing-over the batteries 1a, 1b in a parallel connection or a series connection. The relay 4 contains driving coils 4a, 4b and 4c and contact points 5a, 5b and 5c. Numeral 6 designates a large power electric load (or a large current load) such as an electrically heated catalyst, numeral 7 designates a switch for connecting the batteries to actuate the large power electric load 6, and numeral 8 designates a controller which is connected with control lines 10a, 10b and 10c extending from the relay 4 and controls the driving coils 4a to 4c and the switch 7 at the optimum timing.
FIG. 4 shows a state of normal operation. In such normal operation, the positive side of the battery 1a is connected to the positive side of the battery 1b by means of a contact 5a of the relay 4. Similarly, the negative sides of the batteries 1a and 1b are connected by a contact 5c. Thus, the batteries 1a, 1b are connected in parallel, and they are charged by the charging generator 2 while they supply power to the electric load 3. In FIG. 4, the contacts 5a to 5c of the relay 4 are normal off contacts, namely, they are normally opened when no electric current is supplied to the coils 4a to 4c. The Figure shows that the coils 4a and 4c receive an electric current from the controller 8.
Description will be made as to a case that the large power electric load 6 is to be actuated.
During the above-mentioned normal operation, when the controller 8 judges that a condition for actuating the large power electric load 6 is established, the controller 8 opens the contacts 5a, 5c by stopping a driving current to the coils 4a and 4c of the relay 4, and at the same time, the controller 8 closes the contact 5b by feeding a current to the coil 4b. By the operation of the controller 8, the positive side of the battery 1a and the negative side of the battery 1b are connected each other to thereby form a series connection. At the same time, the switch 7 is closed by means of the controller 8. Then, power is supplied to the large power electric load 6 from the batteries 1a, 1b and the charging generator 2.
When operation of the large power electric load 6 is finished, the switch 7 is opened. The controller 8 stops the supply of current to the coil 4b of the relay 4, and at the same time, the coils 4a, 4b are supplied with a current to close the contacts 5a. 5c whereby the state of normal operation is restored.
The conventional power supply voltage change-over apparatus for a vehicle has, however, the following disadvantage. If a failure of normal opening occurs in either contact of the parallel/series connection change-over relay 4 by an accident such as melting, the controller can not detect the failure. In this case, when the operation of the system is continued, a contact for connecting the positive side and the negative side of the batteries may be closed whereby there is a danger of short-circuiting the batteries.